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Technology : Speedy relief for victims of cyanide poisoning

By Philip Cohen

San Francisco

A MISSHAPEN blood protein could soon save the lives of people poisoned by
cyanide. The protein forms the basis of an experimental test that rapidly
detects the toxin, so that doctors can administer an antidote in precisely the
right dose. If the test proves practical, experts say that smoke inhalation
victims, who are often exposed to cyanide, will be among the first to
benefit.

Paint, plastics and many household chemicals give off cyanide gas when they
burn. So victims of smoke inhalation often have to deal with high levels of
cyanide in their blood, as well as their physical injuries. But doctors rarely
treat the poison, says Avery Tung, a doctor at the University of Chicago in
Illinois, because the antidote, sodium nitrite, works by converting some of the
patient’s haemoglobin to methaemoglobin—a distorted form of protein that
binds tightly to cyanide rather than oxygen. “If you give too much, you can
starve the patient of oxygen, which is adding insult to an already very injured
person,” says Tung.

Doctors could theoretically tailor their dose of sodium nitrite to the level
of cyanide poisoning, but current tests for cyanide can take hours because they
depend on complex chemical reactions or specialised machines that are not
available in some hospitals. “By the time you’d have the answer, the patient who
needed the antidote is probably dead,” says Tung.

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But Tung and his colleague Jonathon Moss realised they could carry out a
rapid analysis in a test tube. It turns out that when methaemoglobin grabs hold
of cyanide it changes colour, from brown to orange. Tung says that the degree of
colour change can be read instantly in a spectrophotometer—which is
available in any hospital lab—and used to accurately measure cyanide
levels in the blood. The two researchers presented preliminary data on the test
last month at a meeting of the American Society of Anesthesiologists in New
Orleans.

Kent Olson, director of the San Francisco poison control centre, says that
doctors would welcome any reliable rapid test. “A very quick test would be
helpful because it could be performed before and after the antidote is given to
see if it is necessary to repeat.”